Bi-adaptive scan digital universal sensor target tracker

ABSTRACT

Two or more concentric scan boundries are used to track small or large objects. A sensor which has multiple detectors, or a detector with multiple readout signals displaced spatially so as to cover the area of concern with overlapping scans is used for scanning. The central area bounded by the scans is used to sense minor variations in relative object movement. The outer bounded area is used to sense large variations which escape the central area, to sense an object which is initially larger than the central area, and to sense an object which has become larger due to range closure. A digital logic circuit is coupled to the sensor output and generates error signals based on the occurence of object video signals coincident with scan derived timing signals.

limited States Patent Todd et al.

ill-ADAPTIVE SCAN DIGITAL UNIVERSAL SENSOR TARGET TRACKER lO/l972 Parkinet al. ..250/203 Primary Examiner-T. H. Tubbesing Att0rney-R. S.Sciascia, G. J. Rubens, J. W. McLaren [75] Inventors: Barry S. Todd,Norco', Werner G. and M Phillips Hueber, China Lake, both of Calif.

[73] Assignee: The United States of America as [57] ABSTRACT "Presentedby the Secretary the Two or more concentric scan boundries are used to ytrack small or large objects. A sensor which has multi- [22] Filed;Jam4, 1971 ple detectors, or a detector with multiple readout signalsdisplaced spatially so as to cover the area of [21] PP N05 103,904concern with overlapping scans is used for scanning. The central areabounded by the scans is used to sense [52] SCI "250/203 l78/DIG' 21250/833 H minor variations in relative object movement. The 343/72343/117 outer bounded area is used to sense large variations [51] Int ClI G015 9/64 which escape the central area, to sense an object Field 4 i6R 6 M which is initially larger than the central area, and to 343/117 563 sense an object which has become larger due to range T closure. Adigital logic circuit is coupled to the sensor [56] References Citedoutput and generates error signals based on the occurence of objectvideo signals coincident with scan UNITED STATES PATEN-TS' derivedtiming Signals- 3,243,804 3/1966 Smith ..343/7.4 1 Claim, 4 DrawingFigures l4 2 3 U. IDE m PRdcEs me SENSOR l4 B IDEO DOWN PR CESSING ILOGIC ERROR I MATRIX SIGNALS l8 C VIDEO l LEFT PROCESSING b SOURCE 1 DVIDEO l a RIGWHT PROCESSING L t L l |s ,os 2O a- B COUNTER IS .osDECODER 3 3 Patented May 1-, 1973 2 Sheets-Sheet 1 4 I6 V I0) A I I UPVIDEO I I PROCESSING SENSOR I DOWN VIDEO 1 PROCESSING LOGIC ERRoR MATRIXSIGNALS LEFT P c z me I SCAN R SOURCE l4 D VIDEO I R'GHT PROCESSINGISA'OSA 20\ COUNTER E2822 DECODER- ISDIOSD INVENTO-RS ATTORNEYS PatentedMay 1, 1973 3,731,104

2 Sheets-Sheet 2 TOP SCAN DERIVED RESET PULSED SEGMENT THREE STAGEDIGITAL COUNTER s s 5 FIG. 3

23 DECODER v I REFERENCE C I VOLTAGE FIG. 4

INVENTORS BARRY S. TODD BY WERNER G. HUEBER 71v. 5446;

r wr A TORNEYS III-ADAPTIVE SCAN DIGITAL UNIVERSAL SENSOR TARGET TRACKERSTATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION Present electro-optical radar and infraredtracking systems which utilize a simple conical shaped scan pattern havea dead area where no information on the exact position of the object tobe tracked is available. Unless provision is made for an adaptable scansize which is difficult to achieve, only an optimum object size to scansize ratio will provide acceptable position information. The presentinvention provides a tracking system which overcomes this limitationwhile retaining the simple scan pattern, scanning speed and processingsimplicity. Two or more concentric scan boundaries are used to trackobjects of different sizes, small objects which become large dueto'range closure, and small objects which have escaped the innerboundry. A large area surrounding the object is scanned providinginformation useful in correlation techniques. A sensor is utilized whichhas multiple detectors, or a detector with multiple readout signalsdisplaced spatially so as to cover the area of concern with overlappingscans. The central area bounded by the scan is used to sense minorvariations in relative object movement. The outer bounded area is usedto sense large variations which escaped the central area, to sense anobject which is initially larger than the central area, and to sense anobject which has become larger due to range closure. A decision ofwhether a signal corresponding to an object is present at any instant oftime is made for each sensor output. Digital logic is then used togenerate the proper pair of signals based on the occurrence of objectvideo signals coincident with scan derived timing signals. These errorsignals or tracking signals-are used to maintain the object within thecentral or outer bounded area.

Accordingly, an object of the invention is to provide an improved targettracking system which is devoid of a dead area for tracking information.

Another object of the invention is to provide an improved targettracking system which generates two or more concentric scan boundriesfor tracking small or large objects.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a block diagram of the preferred embodiment of the invention;

FIG. 2 is a diagram of scans showing how the inner areas and outer areasare formed;

FIG. 3 is a block diagram showing how the signals are derived from thecircular scans of FIG. 2;

FIG. 4 is one form of the video processing circuit of FIG. I.

Referring now to FIG. 1 there is shown in the preferred embodiment inblock diagram a sensor 10 which may consist of a number of detectorsphysically or by electronic means separated spatially with respect tothe field of view 12. Sensor 10 may take the form of a multi-apertureimage disector, a mechanical scan infrared system with multipledetectors, or four reflector/receiver radar array using a singletransmitter with conical scan. Sensor 10 may be constructed to besensitive in any region of the electromagnetic spectrum. Each of thedetector outputs from sensor 10 is connected to a video processingcircuit 14. If a target is present in one of the sectors being scannedan output from video processing circuit 14 corresponding to the detectorfor that particular sector will appear as an output and is fed as asignal input to logic matrix 16. Video processing circuit 14 may be ofthe type shown in FIG. 4 where the output signal from sensor I0 iscompared with a reference voltage 15 by means of comparator 17. Scansource 18 provides the scanning signal to cause sensor 10 to scan in theparticular configuration desired. Scan source 18 also provides thesegment count signal to counter decoder 20 as well as a reset signal.The output of counter decoder 20 provides scan derived timing inputsignals to logic matrix 16.

Referring to FIG. 2 there is shown in diagram form a four circular scan.An inner area is generated where all four scans overlap and an outerarea where there is no overlap. The inner area scan is shown in heavyline and the outer scan segment is shown with a wavey line. The videosignals from each detector are associated with their respective scan,i.e., A, B, C, or D, and with specific scan segments, i.e., in FIG. 3. Avideo output signal at A, FIG. 1, corresponds to the presence of anobject in segment IS or 05,, dependingon what time during the scan thesignal occurred. This is accounted for in the logic derived fromselected rules of the tracking system. One possible set of trackingrules is as follows:

Rule No. Rule Table Entry or Entries 1. If all inner segments crossobject,

no error I 2. If one inner segment does not cross object, error is awayfrom segment. 2-5 3. If two inner segments do not cross object, errorsare away from segments. 6.9 4. If three inner segments do not crossobject, error is away from single segment, cannot determine error indirection of paired segments. Wait until object appears in outersegment. 10-l2 5. If any inner segment crosses object, ignore outersegment information in that same direction. l-13 6. If an inner segmentpair does not cross object use outer segment information in samedirection according to rules 2, 3. l4-l5 Table l is compiled based uponthe above Rules showing the error signals which need to be generated asa function of the object designation signals. Table I on page 5.

TABLE I Video signals presr-nt during, segment signnls--- Error signals(zeros are as sumnd where symbols are missing) number ISA lSn USA US;()Sn S1) Up Down Lolt Right "any combination ere-ecu,-

0 O (l (l t] l (J any (:omli. (I (l FIG. 3 shows a three stage digitalcounter 21 (which may be a three stage flip-flop circuit) which dividesthe circles into eight segments. The output from counter 21 is fed intoa decoder 23 which will provide outputs to satisfy the followingequations.

Where letter with prime 0; letter without prime l.

The implementation of the logic matrix 16 shown at FIG. 1 can be derivedusing traditional combinatorial system design which is well known in theart, i.e., Caldwell, Samuel H., Switching Circuits and Logic Design,Wiley, N.Y., 1958, 119 through 143. The result is a combinatorialnetwork which provides the proper error signals responding to any set ofinputs.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

ll. In a passive electro-optical bi-adaptive scan target tracker havingtwo concentric scan boundries for tracking targets of different sizes,small objects which become large due to range closure, and small objectswhich have escaped the inner boundry, the combina- 25 tion comprising:

an electro optical sensing means having four circularly scanningdetectors capable of scanning an area of concern with over-lappingboundries, scan control means coupled to said sensing means forcontrolling the pattern of scan to generate an inner tracking area onlywhere all scans overlap and an outer area comprised of thenon-overlapping areas, logic matrix means having first and second inputsand having multiple outputs, video processing circuit means coupled tosaid elec tro-optical sensing means and to said first inputs of saidlogic matrix for generating an output video signal whenever an objectappears in the scan area pertaining to that particular video processingcircuit, counter decoder coupled to said scan control means and tov saidsecond inputs of said logic matrix for generating scan derived timingsignals, said logic matrix being responsive to said input video signalsand said scan derived timing signals for generating an output errorsignal according to the location of the target within the area beingscanned by said sensing means.

1. In a passive electro-optical bi-adaptive scan target tracker havingtwo concentric scan boundries for tracking targets of different sizes,small objects which become large due to range closure, and small objectswhich have escaped the inner boundry, the combination comprising: anelectro optical sensing means having four circularly scanning detectorscapable of scanning an area of concern with overlapping boundries, scancontrol means coupled to said sensing means for controlling the patternof scan to generate an inner tracking area only where all scans overlapand an outer area comprised of the nonoverlapping areas, logic matrixmeans having first and second inputs and having multiple outputs, videoprocessing circuit means coupled to said electro-optical sensing meansand to said first inputs of said logic matrix for generating an outputvideo signal whenever an object appears in the scan area pertaining tothat particular video processing circuit, a counter decoder coupled tosaid scan control means and to said second inputs of said logic matrixfor generating scan derived timing signals, said logic matrix beingresponsive to said input video signals and said scan derived timingsignals for generating an output error signal according to the locationof the target within the area being scanned by said sensing means.